It has greater Isp than Hydrogen, greater density than even Propane/H2O2, and thrust second only to the Shuttle SRBs. It's still cryogenic, but as the amount of Hydrogen is lower, it is easier to store. Cost is likely to be on the order of $2-3/kg, but buying in bulk would reduce this somewhat, and besides, it would still allow spaceflight below $100/kg.

Thoughts? If you follow the NewMars link, jumpboy11j has done some size comparisons between Ares V and Ares V-H (Halo). Same payload, but we can ditch the SRBs and first stage.

look up HEDM, and check out some of the crazy fuels that are being proposed. dodecahedral nitrogen, metallic hydrogen, etc... that stuff is awesome. some of the ISPs possible with this stuff approach the ~800isp of nuclear thermal engines. of course, these materials exist only in small amounts in special laboratories now, but who's to say they won't be mass-producible in 5-10 years.